Conventionally, the variable intake system is known to change a length of an intake passage through which intake air is supplied to an internal combustion engine (e.g., a combustion chamber in the internal combustion engine), based on an operation condition of the internal combustion engine. For example, Patent Document 1 (JP-2010-001847 A) and Patent Document 2 (JP-2009-216066 A) describe such a variable intake system.
According to Patent Document 1, a variable intake system has an intake manifold, an intake control valve, and an actuator. The intake manifold includes an annular protruding portion (e.g., an annular valve seat) protruding from an inner surface of an opening part that is provided at a curved wall surface of a connector. The intake control valve includes a valve body that is made of synthetic resin and is formed in a rectangular plate shape. The actuator operates a shaft of the intake control valve. The intake control valve further includes a sealing lip. The sealing lip is made of an elastomer and attached to an outer peripheral surface of the valve body. For example, the sealing lip is adhered to the outer peripheral surface by using an adhesive. When the sealing lip fits tightly to the annular valve seat that protrudes from the inner surface of the opening part, the opening part is fully closed and restricts intake air from leaking.
According to Patent Document 2, an intake control valve of a variable intake system has a valve shaft, a valve body, a base member, and an elastic spacer. The valve shaft is operated by an actuator. The valve body opens or closes a connecting hole provided by a periphery part, which is provided by a partition wall forming a chamber wall or an intake pipe. The base member rotates integrally with the valve shaft and supports the valve body to be relatively movable. The elastic spacer is made of an elastomer which is capable of deforming elastically. The elastic spacer is arranged between the valve body and the base member. The valve body includes a body member and an elastic sealing member. The body member substantially fully closes the connecting hole when the intake control valve is closed. The elastic sealing member is made of an elastomer. The elastic sealing member is arranged at a tip part of the body member and forms a tip part of the valve body. The elastic sealing member includes a sealing lip which is elastically deformed when the sealing lip fits tightly to a front edge of the periphery part provided by the partition wall.
According to Patent Document 1, the intake control valve used in the variable intake system has the valve body and the sealing lip. The valve body is made of the synthetic resin. The sealing lip is made of the elastomer and attached to the outer peripheral surface of the valve body. Therefore, an adhesion process is required to adhere the sealing lip to the outer peripheral surface of the valve body by using the adhesive. Therefore, manufacturing cost increases. The manufacturing cost may decrease when the sealing lip is adhered to the outer peripheral surface of the valve body without using the adhesive. However, adhesive strength of the sealing lip with respect to the outer peripheral surface of the valve body decreases, and the sealing lip may be peeled partly or peeled off from the valve body. Accordingly, a clearance is provided between the valve body and the valve seat when the intake control valve is fully closed, and intake air leaks through the clearance. As the result, while the intake control valve is fully closed, a volume of intake air leaking through the clearance increases. That is, a sealing performance declines.
A thermoplastic elastomers may be used instead of the elastomer forming the sealing lip. However, an adhesive strength between the thermoplastic elastomer and the synthetic resin forming the valve body is lower than an adhesive strength between the elastomer and the synthetic resin. Accordingly, when the sealing lip is made of the thermoplastic elastomer, the sealing lip may separate easily from the valve body. Therefore, a clearance is provided between the valve body and the valve seat when the intake control valve is fully closed, and intake air leaks through the clearance. As the result, a volume of intake air that leaks through the clearance while the intake control valve is fully closed increases. That is, the sealing performance declines.
According to Patent Document 2, the intake control valve used in the variable intake system has the valve body including the body member and the elastic sealing member, the base member, and the elastic spacer. Further, the elastic sealing member is integrally molded with the elastic spacer to form an elastic part that is made of the elastomer and mounted to the intake control valve. Accordingly, manufacturing cost increases due to increase of the number of components and the number of assembly processes.